This invention relates to data communications systems.
This invention also relates to facsimile systems comprising a transmitter, a receiver and a communications network therebetween. More particularly, this invention relates to a system wherein a document is scanned in a facsimile transmitter to generate electrical information-bearing signals representing the dark-light variations in the document being scanned. These information-bearing signals are then transmitted over the communications network to a facsimile receiver where the information-bearing signals are converted to marks or images on a copy medium so as to form a copy which is a reasonable facsimile of the original document.
Typically, the communications network comprises ordinary telephone lines and the transmission over such lines may, at times, become substantially degraded. While such degradation in the quality of transmission can be tolerated in many telephone conversations, a facsimile transmission requires the maintenance of rather high transmission quality if an accurate facsimile or copy is to be obtained.
Heretofore, when a facsimile transmission has produced poor copy, the operator of the facsimile receiver was never really certain if the quality of the transmission had fallen below acceptable levels, the receiver was faulty, the transmitter was faulty or the original document being transmitted was of poor quality. In many cases, the operator has assumed a defective receiver when, in fact, the transmission was at fault, and this has resulted in unnecessary service calls. Where the receiver operator has informed the transmitter operator of the poor quality of the copy, the transmitter operator has, in some instances, initiated unnecessary service calls where the transmission was really at fault.